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Practice Problems
P1.17: An FM radio receiver has an input resistance of 75 Ohm. The input signal provided by a distant
transmitter is 5 µV rms, and the receiver supplies 5 V rms to an 8 Ω loudspeaker. Calculate the
power gain of the receiver.
P1.33: An amplifier has a voltage gain of 30 dB, and a current gain of 70 dB. What is the power gain in dB?
If the input resistance is 100 KΩ, what is the load resistance?
P1.63: A differential amplifier has vo (t) = A1v1(t) – A2v2(t), If A1 = 1000, and A2 = 999, determine the CMRR.
Answers:
P1.17: 9.375 x 1E12
P1.33: GdB = 50, RL = 1 KΩ
P1.63: CMRR = 60 dB
Answer: -20 dB and CMRR = 114 dB
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Chapter 2: The Operational Amplifier (Op Amp)
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The Operational Amplifier continued
Summing Point Constraint:
This concept refers to the fact that under
negative feedback conditions:
(i) The differential input voltage will be zero in ideal
op-amps (or very close to it in non-ideal ones)
as the gain is ideally infinite
(ii) The input current will also be zero as there is no
voltage and the resistance is very high (ideally
infinite)
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The Operational Amplifier continued
Note here that the resistor
R2 provides the negative
feedback to the input of the
op-amp. This means that,
as the i/p voltage increases,
the negative o/p voltage
also increases, and tends to
reduce the input to the opamp by feedback, to
provide a finite gain.
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